Overall device weight is often a significant factor with regard to semiconductor devices used in specialized applications such as aerospace applications, military applications, or other applications where portability of the device is important. Overall device weight is particularly important with regard to large area devices such as photovoltaic devices. Hence, there are significant incentives for the fabrication of large area, lightweight photovoltaic and other semiconductor devices.
Thin film semiconductor materials are frequently used for the preparation of lightweight photovoltaic devices since they are flexible, light in weight, and can be readily deposited over large areas by high speed, efficient deposition processes. In a typical thin film semiconductor device, the substrate, which supports the layers, is the major component of the weight of the device. In those instances where weight is not significant, substrates of glass, ceramic or metal may be employed. However, for lightweight and ultra lightweight applications thin substrates, typically fabricated for polymeric materials or metal foils, are preferred.
The use of thin, lightweight substrates can complicate processes for the fabrication of photovoltaic devices, particularly when those devices are being fabricated in a large volume, high speed process. Therefore, thin, lightweight substrates are frequently used in combination with a relatively thicker support member which is subsequently removed after device fabrication is completed.
In most instances, it is desirable that the positive and negative contact terminals for a photovoltaic device both be located so as to simplify its installation and use. In that regard, it is desirable that the device have electrical connection points that occupy different positions along a cross section of the device. The affixation of current collecting structures such as grid members, bus bars and terminals to a photovoltaic device can be complicated in those instances where a support member is employed. As will be explained hereinbelow, the present invention provides methods and device structures whereby lightweight photovoltaic devices may be fabricated on a thin substrate member, and wherein the devices are configured to have same surface terminals. These and other advantages of the invention will be apparent from the drawings, discussion and description which follow.